<![CDATA[Purpose: Research on environmental costing in public water utilities remains limited, as previous studies mainly focus on manufacturing, energy, and listed firms. Limited evidence explains how environmental cost information interacts with governance mechanisms to improve sustainability outcomes in public utilities. This study examines the effects of environmental costing and good corporate governance (GCG) on sustainability performance and tests the moderating role of GCG at PT Air Minum Jayapura Robongholo Nanwani.Research Methodology: A quantitative explanatory cross-sectional design was conducted from April to July 2026. Using purposive sampling, 66 employees involved in finance, operations, services, reporting, supervision, and governance were selected from 195 employees. Data were collected through questionnaires and company documents and analyzed using Partial Least Squares Structural Equation Modeling (PLS-SEM).Results: Environmental costing and GCG positively and significantly affect sustainability performance. However, the EC × GCG interaction has a negative and significant effect, indicating that GCG weakens the relationship between environmental costing and sustainability performance. This finding shows that governance does not always strengthen environmental practices and depends on how cost information is embedded in decision-making.Conclusions: Environmental costing and GCG independently improve sustainability performance, but their combined effect requires substantive integration into strategic and operational processes.Limitations: The study focuses on one public water utility and uses a cross-sectional design, limiting generalizability and long-term assessment.Contributions: This study extends Environmental Management Accounting and governance literature by providing evidence from an underexplored public utility context and showing that governance quality does not automatically enhance environmental costing outcomes.]]>
